It has been found through scientific studies that expansion of the lungs through inspiration is extremely important in overcoming post-operative pneumonia and atalectasis. There are a number of devices currently available for single patient use which are intended to expand the user's lungs. They are generally referred to as incentive spirometers or incentive deep-breathing exercises. One such device is taught in U.S. Pat. No. 4,037,836 and another in U.S. Pat. No. 4,060,074. These devices comprise one or more vertically disposed chambers, the chambers each containing a lightweight ball, such as a ping pong ball, which is caused to rise as the user inhales through a flexible inhalation tube connected to the chambers. In another form of such device, a lightweight piston is fitted in a chamber in a manner such that withdrawal of the air from the chamber causes upward movement of the piston. Devices of this character measure the rate of air flow, i.e., air flow per second, to give an indication of what the patient is accomplishing in terms of lung expansion.
Researchers have determined that the rate of air flow is not the most satisfactory criteria for determining expansion of the lungs. One can achieve a very rapid air flow by inhaling suddenly, yet not adequately expand the lungs. Consequently the accepted recommendation is that the patient must slowly expand his lung volume, the volume of inhaled air and hence the extent to which the lungs have been expanded being the criteria for determining the effectiveness of the exercise. It is therefore desirable to provide a device which will encourage optimum lung expansion and provide a visual measurement of the volume of air inhaled, thereby providing an accurate indication of the extent to which the lungs have been expanded.